PFPEs having at least an alkylether end group and respective preparation process

ABSTRACT

Perfluoropolyethers having structural formula 
     R 1 O—(CF 2 O) n —(CF 2 CF 2 O) m R 2   (I) 
     wherein:  
     R 1  is —CH 3  or —C 2 H 5 ; R 2  is equal to R 1  or —CF 2 H n is 0 or an integer from 1 to 100; m is an integer from 1 to 100 or, when R 2  is —CF 2 H, m can also be 0; the oxyfluoro-alkylene units —(CF 2 CF 2 O)— and —(CF 2 O)— are statistically distributed along the polymer chain.

[0001] The present invention relates to perfluoropolyethers (PFPE)having at least one alkylether end group and to the respectivepreparation process.

[0002] One of the methods for preparing perfluoropolyethers is thepolymerization of tetrafluoroethylene (TFE) at low temperature,generally between −30° C. and −100° C., with oxygen in the presence ofUV radiations or of radical initiators such for example F₂, CF₃OF, ininert solvent. From said reaction a peroxidic perfluoropolyether isobtained formed by sequences of oxyperfluoroalkylene units —CF₂CF₂O—,—CF₂O—, which contain peroxidic groups —CF₂CF₂O—O—, —CF₂O—O— in variableamounts. Said peroxidic compound is subsequently reduced by physicaltechniques as thermal or photochemical treatment or chemical techniquesas for example reduction with H₂ in the presence of catalysts based onnoble metals (Pt, Pd). The reduction breaks the peroxidicperfluoropolyether bonds and gives perfluoropolyethers having a lowermolecular weight with —COF end groups. See for example U.S. Pat. No.5,354,922.

[0003] One of the problems arising in carrying out said method is theneed to determine the content of peroxidic bonds (PO) present in thePFPE to be reduced. The amount of peroxidic bonds varies depending onthe polymerization reaction conditions. The peroxide content of theperoxidic PFPE has a remarkable importance since it controls thefunctionality degree of the final perfluoropolyethers, besides itsdetermination allows to evaluate that it does not exceed 5% (expressedas active oxygen weight with respect to 100 g of compound) since amountshigher than said value compromise the polymerization plant due to safetyfor possible explosion. It is therefore necessary to continuouslymonitor the PO content during the polymerization reaction.

[0004] Furthermore it is essential to determine the presence even intraces of the peroxidic bonds contained in the final perfluoropolyethersobtained from the reduction of the peroxidic PFPEs, since in their use,for example as lubricants, said content must be lower than 1 ppm, inparticular when they are used in the presence of metals to avoid thedegradation of the perfluoropolyether itself.

[0005] Among the various analytical methods developed for determiningthe PO content in perfluoropolyether chains, a method comprising thetitration of iodine generated by oxidation of an iodide from theperoxide contained in the PFPE, carried out in the presence of aspecific solvent which results compatible with the peroxidic PFPE, hasacquired a prevailing use, for economic reasons, of simplicity andsensitivity. A particularly suitable solvent commonly used in saidmethod is 1,1,2-trichloro trifluoro ethane (CFC 113). See for exampleU.S. Pat. No. 3,770,792.

[0006] However due to the Montreal Conference, chlorofluoro-carbons, asCFC 113, have been banned.

[0007] The need was therefore felt to find a solvent having the samecharacteristics and properties of CFC 113 to be used in the aforesaidanalytical determination.

[0008] It has been unexpectedly and surprisingly found that it ispossible to use in the iodometric determination of the PFPE oxidizingpower (PO), solvents formed by perfluoropolyethers having one end group—CH₃ or —C₂H₅ and the other selected from —CH₃, —C₂H₅, —CF₂H.

[0009] An object of the present invention are thereforeperfluo-ropolyethers having the following structural formula

R₁O—(CF₂O)_(n—(CF) ₂CF₂O)_(m)R₂  (I)

[0010] wherein:

[0011] R₁ is —CH₃ or —C₂H₅;

[0012] R₂ is equal to R₁ or —CF₂H;

[0013] n is 0 or an integer from 1 to 100;

[0014] m is an integer from 1 to 100 or, when R₂ is —CF₂H, m can also be0;

[0015] the oxyfluoroalkylene units —(CF₂CF₂O)— and —(CF₂O)— arestastistically distributed along the polymer chain.

[0016] Among the perfluoropolyethers of formula (I) those having thefollowing structures, or their mixtures, are preferred:

[0017] H₃CO—(CF₂O)_(n)—(CF₂CF₂O)_(m)CH₃

[0018] H₅C₂O—(CF₂O)_(n)—(CF₂CF₂O)_(m)C₂H₅

[0019] H₃CO—(CF₂O)_(n)—(CF₂CF₂O)_(m)CF₂H

[0020] H₅C₂O—(CF₂O)_(n)—(CF₂CF₂O)_(m)CF₂H

[0021] wherein m, n are selected so as to have a number averagemolecular weight lower than 5,000.

[0022] Examples of compounds which are included in said structures arethe following:

[0023] CH₃OCF₂CF₂OCH₃

[0024] CH₃OCF₂CF₂OCF₂CF₂OCH₃

[0025] CH₃OCF₂CF₂OCF₂OCF₂CF₂OCH₃

[0026] CH₃O(CF₂CF₂O)₃CH₃

[0027] CH₃OCF₂CF₂O(CF₂O)₂CF₂CF₂OCH₃

[0028] CH₃OCF₂CF₂OCF₂OCF₂CF₂OCF₂CF₂OCH₃

[0029] CH₃O(CF₂CF₂O )₄CH₃

[0030] CH₃OCF₂CF₂OCF₂O(CF₂CF₂O)₂CF₂CF₂OCH₃

[0031] CH₃OCF₂CF₂OCF₂CF₂OCF₂OCF₂CF₂OCF₂CF₂OCH₃

[0032] CH₃O(CF₂CF₂O )₅CH₃

[0033] C₂H₅OCF₂CF₂OC₂H₅

[0034] C₂H₅OCF₂CF₂OCF₂CF₂OC₂H₅

[0035] C₂H5OCF₂CF₂OCF₂OCF₂CF₂OC₂H₅

[0036] C₂H₅O(CF₂CF₂O)₃C₂H₅

[0037] C₂H₅OCF₂CF₂O(CF₂O)₂CF₂CF₂OC₂H₅

[0038] C₂H₅OCF₂CF₂OCF₂OCF₂CF₂OCF₂CF₂OC₂H₅

[0039] C₂H₅O(CF₂CF₂O )₄C₂H₅

[0040] C₂H₅OCF₂CF₂OCF₂O(CF₂CF₂O)₂CF₂CF₂OC₂H₅

[0041] C₂H₅OCF₂CF₂OCF₂CF₂OCF₂OCF₂CF₂OCF₂CF₂OC₂H₅

[0042] C₂H₅O(CF₂CF₂O)₅C₂H₅

[0043] CH₃OCF₂H

[0044] CH₃OCF₂CF₂OCF₂H

[0045] CH₃OCF₂CF₂OCF₂OCF₂H

[0046] CH₃OCF₂CF₂O)₂CF₂H

[0047] CH₃OCF₂CF₂O(CF₂O)₂CF₂H

[0048] CH₃OCF₂CF₂OCF₂OCF₂CF₂OCF₂H

[0049] CH₃OCF₂CF₂OCF₂CF₂OCF₂OCF₂H

[0050] CH₃O(CF₂CF₂O)₃CF₂H

[0051] CH₃OCF₂CF₂OCF₂O(CF₂CF₂O)₂CF₂H

[0052] CH₃OCF₂CF₂OCF₂CF₂OCF₂OCF₂CF₂OCF₂H

[0053] CH₃O(CF₂CF₂O)₃CF₂OCF₂H

[0054] CH₃O(CF₂CF₂O)₄CF₂H

[0055] C₂H₅OCF₂H

[0056] C₂H₅OCF₂CF₂OCF₂H

[0057] C₂H₅OCF₂CF₂OCF₂OCF₂H

[0058] C₂H₅O(CF₂CF₂O)₂CF₂H

[0059] C₂H₅OCF₂CF₂O(CF₂O)₂CF₂H

[0060] C₂H₅OCF₂CF₂OCF₂OCF₂CF₂OCF₂H

[0061] C₂H₅O(CF₂CF₂O)₂CF₂OCF₂H

[0062] C₂H₅O(CF₂CF₂O)₃CF₂H

[0063] C₂H₅OCF₂CF₂OCF₂O(CF₂CF₂O)₂CF₂H

[0064] C₂H₅OCF₂CF₂OCF₂CF₂OCF₂OCF₂CF₂OCF₂H

[0065] C₂H₅O(CF₂CF₂O)₃CF₂OCF₂H

[0066] C₂H₅O(CF₂CF₂O)₄CF₂H

[0067] As said the perfluoropolyethers of formula (I), optionally inadmixture with each other, can unexpectedly be used as solvents insubstitution of CFC 113 in the iodometric detrmination of the PFPEoxidizing power (PO). Examples of PFPE which can be analyzed for the POdetermination are those having the repeating units —CFX₁O— and—CF₂CFX₁O—, wherein X₁ is —F or —CF₃.

[0068] The perfluoropolyethers of formula (I) are characterized by beingenvironmental friendly since they have an ozone impact equal to zero(ODP=0) and a very low potential greenhouse effect (GWP).

[0069] The Applicant has found that the perfluoropolyethers of theinvention can be used also for the further following applications. Theperfluoropolyethers of formula (I), optionally in admixture with eachother, due to their high solvent power for the perfluoropolyetherlubricants, in particular those containing repeating units —CFX₁O— and,—CF₂CFX₁O—, wherein X₁ is —F or —CF₃, are particularly suitable to beused as solvents in the acidity determination of said lubricants. Forthis purpose the perfluoroether oil is dissolved in the compounds offormula (I), added with an aqueous solution of NaOH and the base excessis potentiometrically titrated with hydrochloric acid.

[0070] The perfluoropolyethers of formula (I) can also be used assolvents in the determination of arsenic traces and heavy metals in casepresent in perfluoropolyether oils, in particular those used in cosmeticpreparations for which the substantial absence of said metals isrequired, since they can cause dermatic allergies. In particular theycan be used as solvents in the ICP-OES (Inductively CoupledPlasma-Optical Emission Spectrometry) method.

[0071] A further application of the perfluoropolyethers of formula (I)is their use as solvents of perfluoropolyether oils having highmolecular weight employrd in lubrication of computer hard disks.

[0072] Due to their high thermal capacity, their UV transparence andtheir chemical inertia the compounds of formula (I) can also be used asrefrigerants which absorb the infrared radiation and remove the heatemitted by UV lamps used in photochemical reactions carried out at lowtemperatures, from −30° C. to −100° C., thus allowing to maintain thelow temperatures used in the reaction reactor. An example of saidphotochemical reaction is the tetrafluoroethylene (TFE) and/orhexafluoropropene (HFP) polymerization with oxygen in the presence of UVradiations.

[0073] The compounds of formula (I) of the present invention in view oftheir chemical, physical properties and of a low impact on theenvironment, find also application in the following fields:

[0074] heat transfer, e.g. in pharmaceutical equipments as lyophilizers

[0075] refrigerants in secondary loop refrigerants

[0076] as lubricants (fluids and greases)

[0077] solvents and/or co-solvents, optionally in the presence ofspecific additives, for cleaning and/or drying components in precisionmechanics, in jeweller's ware/silverware, in opctis

[0078] working fluids in the Thermal Shock tests to which electroniccomponents are subjected, they also are employed in other tests used inelectronics such for example in Gross Leak test, in Burn-in test, inEnvironmental test screening (ESS) and in the hermeticity closure testof a sealed hollow.

[0079] A further object of the present invention is the process for thepreparation of the compounds of formula (I).

[0080] It is known from patent application WO 96/22129 the preparationof perfluorinated compounds containing in the polymer chain oxygenheteroatoms and having alkylether end groups, by alkylation withsuitable alkylating agents, in particular dimethylsulphate, of thecorresponding alkaline alcoholates in their turn obtained by treatmentwith an alkaline metal fluoride, for example KF, in an aprotic polarsolvent, of the corresponding perfluorinated compounds having —COF endgroups. The dimethylsulphate use owing to its toxicity and carcinogenicactivity, raises sanitary and ecological problems. Besides it is hardlyrecoverable from the reaction. Furthermore it is to be used atalkylation temperatures lower than 20° C., wherein also the undesiredformation of a gel is obtained, this due to the reaction between theacylfluorides and the formed alcoholate, with consequent increase of thereaction viscosity and respective remarkable reduction of the alkylationrate.

[0081] The Applicant has found that it is possible to use the abovemethod in the preparation of the perfluoropolyethers of formula (I) byusing particular alkylating agents characterized by:

[0082] not carcinogenic activity

[0083] usable at high temperatures and therefore able to avoid the gelformation

[0084] easy to separate from the reaction system so that they can beregenerated and reused in the process.

[0085] The Applicant has indeed unexpectedly and surprisingly found thatalkylating agents having the above mentioned properties are formed byalkylsulphites or polymers having as repeating units theperfluoropolyoxyalkylene sulphonic esters.

[0086] A further object of the present invention is a process for thepreparation of perfluoropolyethers having structural formula (I)comprising the following steps:

[0087] a) reaction between:

[0088] a perfluoropolyether having -COF end groups of formula

FOCCF₂O—(CF₂O)_(n)—(CF₂CF₂O)_(m)—CF₂COF  (II)

[0089] wherein n, m are integers from 0 to 100,

[0090] or

[0091] a compound of formula

FOC—COF  (II bis);

[0092] with an alkaline metal fluoride (M), in an aprotic polar solvent,at temperatures between 40° C. and 70° C., to yield the correspondingalcoholate having —CF₂OM end groups;

[0093] b) addition to the reaction compound obtained in step a) of analkylating agent:

[0094] an alkylsulphite of formula

(R₁O)₂SO  (III)

[0095] wherein R₁ is —CH₃ or —C₂H₅,

[0096] or:

[0097] a polymer having as repeating units perfluorooxy-alkylenesulphonic esters, of formula (IV)

[0098]  wherein R₁ has the above meaning; the coefficients a, b, c, d,e, f are integers, including zero, with at least a or b different from0, so that their sum is such that the number average molecular weight bein the range 1,000-50,000; T₁, T₂ equal to or different from each other,are selected from —CF₂H, —CF₂X (X=—F, —CF₃, —Cl), —C₃F₇,

[0099] keeping the reaction mixture under stirring, at a temperature inthe range 110° C.-200° C., preferably 130° C. 160° C., when thealkylsulphite (III) is used, and at temperatures in the range 0° C.-60°C., preferably 20° C.-40° C., when perfluoropolyoxyalkylene sulphonicesters (IV) are used;

[0100] c) the reaction mixture-obtained in step b) is salified with abase, preferably KOH or NaOH, then it is distilled in steam flowobtaining an aqueous residue and a distillate from which an organicphase formed by the compound of formula (I) wherein R₁ and R₂ are methylor ethyl, is separated;

[0101] d) the distillation residue of step c) is acidified with a HClsolution, distilled under vacuum, in a range from 70° C. to 170° C.,separating from the distillate an organic phase formed by a compound offormula (I) wherein R₁ is —CH₃ or —C₂H₅ and R₂ is —CF₂COOH, thensalification with KOH or NaOH, subsequently decarboxylated by knownmethods obtaining the compound of formula (I) wherein R₁ is —CH₃or —C₂H₅and R₂ is —CF₂H.

[0102] As alkaline metal fluoride the potassium fluoride (KF) ispreferred.

[0103] As aprotic polar solvent, the diethylenglycol dimethyl-ether(diglyme) is preferred.

[0104] Compared to the alkylation processes with dimethylsulphate of theprior art:

[0105] the use of alkyl sulphites of formula (III), not consideredcarcinogenic, allow to carry out the reaction at temperatures higherthan 100° C., with the advantage that at said temperatures the formationof undesired gel is reduced and an increase of the reaction rate isobtained

[0106] the use of the perfluoropolyoxyalkylene sulphonic ester offormula (IV) has the advantage that it is possible to recover it fromthe reaction mixture as alkaline salt and subsequently to regenerate itby reaction with methanol or ethanol and SOCl₂.

[0107] The Applicant has furthermore found that in the above mentioneduses, besides the compounds of formula (I), also the perfluoropolyetherscan be used, formed by oxyfluoroalkylene units —(CF₂CF₂O)— and —(CF₂O)—statistically distributed along the polymer chain having both end groupsformed by the OCF₂H group described for example in EP 695,775, inparticular the compound sold by the Applicant as GALDEN™ ZT resultssuitable.

[0108] Some Examples follow for illustrative and not limitative purposesof the present invention.

EXAMPLES Example 1

[0109] In a 1000 ml reactor equipped with mechanical stirring andfluxing system with nitrogen, 70 g of anhydrous KF and 600 ml of diglymeare charged. By maintaining the reaction temperature at 20° C., 212 g ofa perfluoropolyether having fluoroacyl end groups of formula (IT)

FOC—CF₂O—(CF₂O)_(n)—(CF₂CF₂O)_(m)CF₂—COF  (II)

[0110] are slowly added, wherein m/n=2.6 and the number averagemolecular weight is 580.

[0111] Said perfluoropolyether has been prepared by photooxidation oftetrafluoroethylene with oxygen and subsequent reduction of the obtainedperoxide.

[0112] The reaction mixture is heated to 60° C. and maintained understirring for 2 hours.

[0113] After having cooled the mixture to 20° C., 130 g ofdimethylsulphite are added.

[0114] When the dimethylsulphite addition is over, the reaction mass iskept under stirring for one hour at room temperature.

[0115] Always under stirring the temperature is brought to 150° C. andit is maintained for two hours.

[0116] At the end, it is cooled to 20° C., and the reaction mixture isneutralized with an aqueous solution of KOH at 10%.

[0117] The reaction mixture is subjected to distillation in steam flowobtaining an aqueous phase and an organic phase formed by a neutralfluorinated compound.

[0118] The fluorinated organic phase is separated, washed with water andanhydrified with calcium chloride.

[0119] 39 g (yield 18%) of a compound which has been characterized byNMR ¹⁹F, ¹H and IR analyses, are obtained. The compound has thefollowing structure:

CH₃OCF₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CF₂OCH₃  (IIa)

[0120] with a m/n ratio=2.6 and a number average molecular weight of576.

[0121] The distillation residue is acidified with 1,000 g of HCl at 20%.

[0122] A fluorinated organic phase is separated which is washed withother 500 g of HCl at 20% and then distilled. 89 g (yield 41%) arerecovered of a fraction which distils between 70° C. and 120° C. at 0.5mbar, characterized by NMR ¹⁹F and ¹H analyses, having the followingstructure:

CH₃OCF₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂COOH  (IIb)

[0123] wherein m/n=2.6 and the number average molecular weight is 585.

[0124] The residue (78 g) is mainly formed by a perfluoropolyetherhaving the two carboxylic end groups of formula

HOOC—CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂COOH  (IIc)

[0125] wherein m/n=2.6.

[0126] Decarboxylation

[0127] 50 g of the acid monofunctional compound of formula (IIb) areneutralized with 100 g of KOH at 5%. The homogeneous solution is chargedinto a 500 ml AISI autoclave, stirred and heated at 160° C. for 8 hours.At the end the mixture is discharged in a separatory funnel.

[0128] 39 g of an organic phase are separated, which after washing withwater and subsequent anhydrification with calcium chloride, has beencharacterized by NMR ¹⁹F, ¹H analyses as a compound having the followingstructure:

CH₃OCF₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂H  (IId)

[0129] having m/n=3.1 and a number average molecular weight of 571.

[0130] The compound (IIa) having the structure

CH₃OCF₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CF₂OCH₃

[0131] shows the following properties: Tg measured by DSC: −125.6° C.Dielectric constant: 5.3 at 1 kHz Boiling point:  155.5° C. Refractiveindex: 1.2935 at 20° C.

[0132] and density and viscosity variations in function of the asreported in the following Table: Temperature (° C.) Density (g/cc)Viscosity (cSt) 40 1.5815 1.37 20 1.6227 2.04 −10 1.6845 4.70

Example 2

[0133] a) Preparation of the Alkylating Agent Methyl Ester of thePolysulphonic PFPE

[0134] 300 g of polysulphonic PFPE having structure (A) were prepared:

T₃O(CF(OCF₂CF₂SO₂F)O)_(a)(CF₂CF(OCF₂CF₂SO₂F)O)_(b)(CF₂O)_(C)T₂  (A)

[0135] wherein T₃, T₂ is

[0136] for 11% molar —CF₃,

[0137] for 82% molar —CF₂COF,

[0138] for 7% molar —CF₂Cl,

[0139] wherein, considering the statistical distribution of theoxyfluoroalkylene units in the polymer chain, it results, on an averagevalue, a=10.6, b=10.1, c=13.2 and a number average molecular weight of6670 and an equivalent weight equal to 309, by photooxidation ofCF₂=CFOCF₂CF₂SO₂F with oxygen and subsequent reduction of the obtainedperoxide.

[0140] 100 g of said compound are treated at 80° C. with 250 g of anaqueous solution of KOH at 20%. The obtained homogeneous solution isneutralized with HCl at 10% and then concentrated under vacuum at thetemperature of 160° C. obtaining 170 g of a solid residue.

[0141] The residue is dispersed in 300 ml of methanol to which 60 g ofSOCl₂ are added.

[0142] The solution is filtered to remove the inorganic salts present asbottom body and the filtrate is distilled under vacuum (0.3 mbar) at thetemperature of 130° C.

[0143] 103 g of a compound are obtained, which characterized by NMR ¹⁹F,¹H and IR analyses, results to have the following structure (B):

T₁O(CF(OCF₂CF₂SO₂OCH₃)O)_(a)(CF₂CF(OCF₂CF₂SO₂OCH₃)O)_(b)(CF₂O)_(c)T₂  (B)

[0144] wherein T₁,T₂ represent on an average value,

[0145] —CF₃ for 11% molar,

[0146] —CF₂H for 82% molar,

[0147] —CF₂Cl for 7% molar,

[0148] wherein on an average value a=10.6, b=10.1, c=13.2 and the numberaverage molecular weight is 6,920.

[0149] b) Methylation of the Diacylfluoride

[0150] In a 1,000 ml reactor equipped with mechanical stirring andfluxing system with nitrogen, 23 g of anhydrous KF and 500 ml of diglymeCH₃O(CH₂CH₂O)₂CH₃ are charged.

[0151] By keeping the temperature at 20° C., 90 g of diacylfluoride offormula (II) of Example 1 are slowly added.

[0152] The obtained mixture is maintained under stirring at 60° C. for 2hours.

[0153] At the end of the two hours the mixture is cooled to −10° C. and100 g of methyl ester of the polysulphonic PFPE of formula (B) preparedat point a) are slowly added.

[0154] When said addition is over, the reactor temperature is brought to40° C. and the mixture is left under stirring for 8 hours. The reactionmixture is then distilled under vacuum (0.3 mbar) up to a temperature of150° C. obtaining a residue and a distillate.

[0155] To the residue, comprising the potassium salt of polysulphonicPFPE, 300 ml of methanol and subsequently 60 g of SOCl₂ are added. Thesolution is filtered to separate the inorganic salts and the filtrate isdistilled under vacuum (0.3 mbar) up to the temperature of 130° C.

[0156] The so obtained methyl ester of the polysulphonic PFPE is usablefor a subsequent methylation.

[0157] The distillate is neutralized with an aqueous solution of KOH at10%. The obtained solution is distilled in steam flow obtaining anaqueous phase and an organic phase formed by a neutral fluorinatedcompound.

[0158] The fluorinated organic phase is separated, washed with water andanhydrified with calcium chloride. 75 g are obtained of a compound whichcharacterized by NMR ¹⁹F, ¹H and IR analyses, results to have thefollowing structure:

CH₃OCF₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CF₂OCH₃

[0159] wherein m/n=2.5 and the number average molecular weight is 601.

[0160] The distilaltion residue has been acidified with 500 g of a HClsolution at 20%.

[0161] A fluorinated organic phase is separated which is washed withother 250 g of a HCl solution at 20% and then distilled. 9.6 g of afraction which distils between 70° C. and 120° C. at 0.5 mbar arerecovered.

[0162] The distilled fraction, characterized by NMR ¹⁹F and ¹H analyses,results to be the compound:

CH₃OCF₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂COOH

[0163] wherein m/n=2.7 and the number average molecular weight is 581.

Example 3

[0164] a) Preparation of the Alkylating Agent Ethyl Ester of thePolysulphonic PFPE

[0165] 98 g of compound (A) described in Example 2 are treated at 80° C.with 250 g of an aqueous solution of KOH at 20%. The obtainedhomogeneous solution is neutralized with a HCl solution at 10% and thenconcentrated under vacuum at the temperature of 160° C. obtaining 164 gof a solid residue.

[0166] The residue is dispersed in 400 ml of ethanol to which 60 g ofSOCl₂ are added. The solution is filtered to eliminate the presentinorganic salts and the filtrate is distilled under vacuum at thetemperature of 130° C.

[0167] 106 g of distillate are obtained, which, characterized by NMR¹⁹F, ¹H and IR analyses results to have the following structure (C):

T₁O(CF(OCF₂CF₂SO₂OC₂H₅)O)_(a)(CF₂CF(OCF₂CF₂SO₂OC₂H₅)O)_(b)(CF₂O)_(c)T₂  (C)

[0168] wherein T₁, T₂ represent on an average value

[0169] —CF₃ for 11% molar,

[0170] —CF₂H for 82% molar,

[0171] —CF₂Cl for 7% molar,

[0172] wherein on an average value a=10.6, b=10.1, c=13.2 and with anumber average molecular weight of 7,210.

[0173] b) Ethylation of the Diacylfluoride

[0174] In a 1000 ml reactor equipped with mechanical stirring andfluxing system with nitrogen, 25 g of anhydrous KF and 500 ml of diglymeCH₃O(CH₂CH₂O)₂CH₃ are charged.

[0175] By keeping the temperature at 20° C., 85 g of diacylfluorde offormula (II) of Example 1 are slowly added.

[0176] The obtained mixture is maintained under stirring at 60° C. for 2hours. At the end of the two hours the mixture is cooled to −10° C. and101 g of ethyl ester of the polysulphonic PFPE of formula (C) preparedat point a) are slowly added.

[0177] When said addition is over, the reactor temperature is brought to40° C. and the mixture is left under stirring for 8 hours. The reactionmixture is then distilled under vacuum (0.3 mbar) up to a temperature of150° C. obtaining a residue and a distillate.

[0178] The residue is treated according to the above procedure ofExample 2 obtaining the ethyl ester of the polysulphonic PFPE whichresults usable for a subsequent alkylation.

[0179] The distillate is neutralized with an aqueous solution of KOH at10%. The obtained solution is distilled in steam flow obtaining anaqueous phase and an organic phase formed by a neutral fluorinatedcompound.

[0180] The fluorinated organic phase is separated, washed with water andanhydrifiled with calcium chloride. 79 g are obtained of a compoundwhich characterized by NMR ¹⁹F, ¹H and IR analyses, results to have thefollowing structure:

C₂H₅OCF₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CF₂OC₂H₅  (IIe)

[0181] wherein m/n=2.5 and the number average molecular weight is 665.

[0182] The distillation residue has been acidified with 500 g of a HClsolution at 20%. A fluorinated organic phase is separated which iswashed with other 250 g of a HCl solution at 20% and then distilled.11.5 g of a fraction which distils between 70° C. and 120° C. at 0.5mbar, are recovered.

[0183] The distilled fraction, characterized by NMR ¹⁹F and ¹H analyses,results to be the compound:

C₂H₅OCF₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂COOH  (IIf)

[0184] wherein m/n=2.6 and the number average molecular weight is 620.

Example 4

[0185] Analysis of the Oxidizing Power (PO) of a CommercialPerfluoropolyether Fluid

[0186] a beaker adaptable to the DL40 titrator head by Mettler, 20 g ofa perfluoropolyether commercially known as Fomblin® M60 produced byAUSIMONT S.p.A. are weighed with the of 0.001 g.

[0187] 20 ml of solvent formed by the compound (IIa) described inExample 1 and 1 ml of acetic acid are added by pipette. The beaker isconnected to the titration head already equipped with stirrer, platinumelectrode and reference electrode, burette caps for the NaI andthiosulphate solutions.

[0188] 30 ml of NaI solution in isopropanol at 5% by weight are addedand it is put under strong stirring for 15 minutes. The titrationenvironment must be strictly closed and the beaker sheltered from light.

[0189] 10 ml of distilled water are added by pipette and one titres withthe sodium thiosulphate 0,01N solution. A control test withhout theperfluoropolyether to be analyzed and a comparative test using CFC 113as solvent are parallelly carried out.

[0190] The oxidizing power PO (expressed as mg of active oxygen for 1000g of compound) is given by the formula:

PO=(V−B)*0,01*8*1000/P

[0191] wherein:

[0192] V=ml of titrant used to titre the sample

[0193] B=ml of titrant used to titre the control test

[0194] P=weight in grams of the sample.

[0195] The results of the analysis carried out using the two solventsare reported in Table I. TABLE I P V B PO Solvent (g) (ml) (ml) (ppm)CFC 113 20.1005 0.15 0.1 <1 Compound (IIa) 20.1523 0.2 0.1 <1

Example 5

[0196] Analysis of a Perfluoropolyether Containing Traces of Peroxide

[0197] According to the procedure described in Example 4 aperfluoropolyether sample of the productive line Fomblin Z® is analyzed,coming from the thermal treatment section at 230° C. for 6 hours of theperoxidic perfluoropolyethers of the industrial plant. The results arereported in Table II. TABLE II P V B PO Solvent (g) (ml) (ml) (ppm) CFC113 20.2037 5.39 0.1 21 Compound (IIa) 20.3040 5.83 0.1 23

[0198] On the basis of the obtained results, the compound is notsuitable to be sold since it has a PO higher than 1 ppm and therefore itis subjected to a further thermal treatment at 240° C. for 4 hours atthe end of which it results to have a PO lower than 1 ppm analyzedaccording to Example 4 using both CFC 113 and the compound (IIa).

Example 6

[0199] Analysis of the PO of a Peroxidic Perfluoropolyether

[0200] A sample of peroxidic perfluoropolyether is drawn at the outletof the photooxidation reactor with oxygen of tetrafluoroethylene.

[0201] It, after complete evaporation of the reaction solvent, has beenanalyzed according to the procedure described in Example 4 except that 2g of sample and a sodium thiosulphate 0,1N have ben used as titrant.

[0202] Considering the high content of PO it is not necessary to carryout the control test and the formula to determine the PO becomes:

PO=V*0,1*8*1000/P

[0203] wherein

[0204] V=ml of titrant used to titre the sample P=weight in grams of thesample.

[0205] The results of the analysis carried out using the two solventsare reported in Table I.

[0206] The results are reported in Table III. TABLE III P V PO Solvent(g) (ml) (ppm) CFC 113 0.2805 14.9 42,250 Compound (IIa) 0.1834 9.842,250

1. Perfluoropolyethers having structural formulaR₁O—(CF₂O)_(n)—(CF₂CF₂O))_(m)R₂  (I) wherein: R₁ is —CH₃ or —C₂H_(5;) R₂is equal to R₁ or —CF₂H; n is 0 or an integer from 1 to 100; m is aninteger from 1 to 100 or, when R₂ is —CF₂H, m can also be 0; theoxyfluoroalkylene units —(CF₂CF₂O)— and —(CF₂O)— are statisticallydistributed along the polymer chain.
 2. Perfluoropolyethers according toclaim 1, having a structure selected from the group formed by:H₃CO—(CF₂O)_(n)—(CF₂CF₂O)_(m)CH₃; H₅C₂O—(CF₂O)_(n)—(CF₂CF₂O)_(m)C₂H₅;H₃CO—(CF₂O)_(n)—(CF₂CF₂O)_(m)CF₂H; H₅C₂O—(CF₂O)_(n)—(CF₂CF₂O)_(m)CF₂H;wherein m, n are selected so as to have a number average molecularweight lower than 5,000, or mixtures thereof.
 3. Perfluoropolyethersaccording to claims 1-2, selected from the group formed by:CH₃OCF₂CF₂OCH₃ CH₃OCF₂CF₂OCF₂CF₂OCH₃ CH₃OCF₂CF₂OCF₂OCF₂CF₂OCH₃CH₃O(CF₂CF₂O)₃CH₃ CH₃OCF₂CF₂O(CF₂O)₂CF₂CF₂OCH₃CH₃OCF₂CF₂OCF₂OCF₂CF₂OCF₂CF₂OCH₃ CH₃O(CF₂CF₂O)₄CH₃CH₃OCF₂CF₂OCF₂O(CF₂CF₂O)₂CF₂CF₂OCH₃CH₃OCF₂CF₂OCF₂CF₂OCF₂OCF₂CF₂OCF₂CF₂OCH₃ CH₃O(CF₂CF₂O)₅CH₃C₂H₅OCF₂CF₂OC₂H₅ C₂H₅OCF₂CF₂OCF₂CF₂OC₂H₅ C₂H₅OCF₂CF₂OCF₂OCF₂CF₂OC₂H₅C₂H₅O(CF₂CF₂O)₃C₂H₅ C₂H₅OCF₂CF₂O(CF₂O)₂CF₂CF₂OC₂H₅C₂H₅OCF₂CF₂OCF₂OCF₂CF₂OCF₂CF₂OC₂H₅ C₂H₅O(CF₂CF₂O)₄C₂H₅C₂H₅OCF₂CF₂OCF₂O(CF₂CF₂O)₂CF₂CF₂OC₂H₅C₂H₅OCF₂CF₂OCF₂CF₂OCF₂OCF₂CF₂OCF₂CF₂OC₂H₅ C₂H₅O(CF₂CF₂O)₅C₂H₅ CH₃OCF₂HCH₃OCF₂CF₂OCF₂H CH₃OCF₂CF₂OCF₂OCF₂H CH₃O(CF₂CF₂O)₂CF₂HCH₃OCF₂CF₂O(CF₂O)₂CF₂H CH₃OCF₂CF₂OCF₂OCF₂CF₂OCF₂HCH₃OCF₂CF₂OCF₂CF₂OCF₂OCF₂H CH₃O(CF₂CF₂O)₃CF₂HCH₃OCF₂CF₂OCF₂O(CF₂CF₂O)₂CF₂H CH₃OCF₂CF₂OCF₂CF₂OCF₂OCF₂CF₂OCF₂HCH₃O(CF₂CF₂O)₃CF₂OCF₂H CH₃O(CF₂CF₂O)₄CF₂H C₂H₅OCF₂H C₂H₅OCF₂CF₂OCF₂HC₂H₅OCF₂CF₂OCF₂OCF₂H C₂H₅O(CF₂CF₂O)₂CF₂H C₂H₅OCF₂CF₂O(CF₂O)₂CF₂HC₂H₅OCF₂CF₂OCF₂OCF₂CF₂OCF₂H C₂H₅O(CF₂CF₂O)₂CF₂OCF₂H C₂H₅O (CF₂CF₂O)₃CF₂HC₂H₅OCF₂CF₂OCF₂O(CF₂CF₂O)₂CF₂H C₂H₅OCF₂CF₂OCF₂CF₂OCF₂OCF₂CF₂OCF₂HC₂H₅O(CF₂CF₂O)₃CF₂OCF₂H C₂H₅O(CF₂CF₂O )₄CF₂H or mixtures thereof.
 4. Aprocess for the preparation of perfluoropolyethers of claims 1-3,comprising the following steps: a) reaction between: aperfluoropolyether having —COF end groups of formulaFOCCF₂O—(CF₂O)_(n)—(CF₂CF₂O)_(m)—CF₂COF  (II) wherein n, m are integersfrom 0 to 100, or a compound of formula FOC—COF  (II bis);  with analkaline metal fluoride (M), in an aprotic polar solvent, attemperatures between 40° C. and 70° C., to yield the correspondingalcoholate having —CF₂OM end groups; b) addition to the reactioncompound obtained in step a) of an alkylating agent: an alkylsulphite offormula (R₁O)₂SO  (III) wherein R₁ is —CH₃ or —C₂H₅, or: a polymerhaving as repeating units perfluorooxy-alkylene sulphonic esters, offormula (IV)

 wherein R₁ has the above meaning; the coefficients a, b, c, d, e, f areintegers, including zero, with at least a or b different from 0, so thattheir sum is such that the number average molecular weight be in therange 1,000-50,000; T₁, T₂ equal to or different from each other, areselected from —CF₂H, —CF₂X (X=—F, —CF₃, —Cl), —C₃F₇,

 keeping the reaction mixture under stirring, at a temperature in therange 110° C.-200° C., preferably 130° C.-160° C., when thealkylsulphite (III) is used, and at temperatures in the range 0° C.-60°C., preferably 20° C.-40° C., when perfluoropolyoxyalkylene sulphonicesters (IV) are used; c) the reaction mixture obtained in step b) issalified with a base, preferably KOH or NaOH, then it is distilled insteam flow obtaining an aqueous residue and a distillate from which anorganic phase formed by the compound of formula (I) wherein R₁ and R₂are methyl or ethyl, is separated; d) the distillation residue of stepc) is acidified with a HCl solution, distilled under vacuum, in a rangefrom 70° C. to 170° C., separating from the distillate an organic phaseformed by a compound of formula (I) wherein R₁ is —CH₃ or —C₂H₅ and R₂is —CF₂COOH, then salification with KOH or NaOH, subsequentlydecarboxylated by known methods obtaining the compound of formula (I)wherein R_(I) is —CH₃ or —C₂H₅ and R₂ is —CF₂H.
 5. A process accordingto claim 4, wherein as alkaline metal fluoride the potassium fluoride(KF) is used and as aprotic polar solvent, diethylenglycol dimethylether(diglyme) is used.
 6. Use of perfluoropolyethers according to claims1-3, as solvent, in substitution of 1,1,2-trichloro trifluoro ethane, inthe iodometric determination of the peroxidic perfluoropolyetheroxidizing power (PO), preferably those having repeating units —CFX₁O—and —CF₂CFX₁O—, wherein X₁ is —F or —CF₃.
 7. Use of perfluoropolyethersaccording to claims 1-3, as solvent in the acidity determination ofperfluoropolyether lubricants.
 8. Use of perfluoropolyethers accordingto claims 1-3, as solvent in the determination of arsenic traces and ofheavy metals in perfluoropolyether oils, in particular those used incosmetic preparations.
 9. Use of perfluoropolyethers according to claims1-3, as solvent of perfluoropolyether oils having high molecular weightemployed in the lubrication of computer hard disks.
 10. Use ofperfluoropolyethers according to claims 1-3, as refrigerants of UV lampsused in photochemical reactions carried out at low temperatures, from−30° C. to −100° C.
 11. Use of perfluoropolyethers according to claims1-3, in the thermal exchange.
 12. Use of perfluoropolyethers accordingto claims 1-3, as refrigerants in secondary loop refrigerants.
 13. Useof perfluoropolyethers according to claims 1-3, as oils for lubricationor for the preparation of lubricant greases.
 14. Use ofperfluoropolyethers according to claims 1-3, as solvents and/orco-solvents for cleaning and/or drying components in precisionmechanics.
 15. Use of perfluoropolyethers acording to claims 1-3, asworking fluids in electronics for the Thermal Shock tests, Gross Leaktest, in Burn-in test, in Environmental test screening (ESS) and in thehermetic closure test of a sealed hollow.